Implementation and long term experiences with a continuous hygienisation process in food industry - A case study

A three tonne/hour batch-type hygienisation process for animal waste was replaced by a fully continuous process including heat integration. The plant is embedded into a pig abattoir including an anaerobic digestion (biogas) plant and gas-engine-based combined heat and power (CHP) production. Pre-heating is done in a series of four tube bundle apparatuses with heat transferred from the hot treated animal waste leaving the hygienisation plant. A closed water loop is used for heat transfer in this heat recovery arrangement. After pre-heating, the feed passes a second series of four tube bundles operated with heat from the biogas CHP plant in order to meet a target temperature of 72 degrees C at the inlet of the continuous hygienisation section. The material leaving the tube section is finally cooled in a series of four tube bundles and provides heat for pre-heating the feed before it is directed into the biogas plant. The process was started up in 2011 and monitoring results are be presented from 2011 to 2016. With the implementation of the continuous process, energy consumption of the hygienisation step was reduced by 64% for thermal and by 69% for electric energy.